The present invention relates to a concentrator for focusing solar radiation onto an elongate absorber such as in a solar-thermal power plant, for example.
Solar collectors often use trough systems. Such systems comprise an elongate through-shaped concentrator that usually has a parabolic cross section. The absorber, through which a heat transfer medium circulates, is of tubular shape and is arranged in the focal line of the concentrator. The reflectors of these concentrators are most often made of self-supporting composite glass silvered on the rear surface. At a thickness of 6 to 8 mm, these glass mirrors are rather heavy which becomes evident in particular with great aperture widths that extend to up to 6 m. Due to the self-supporting properties of the composite glass, the support structures for these reflectors merely have to support the weight of the reflectors. A shaping support of the reflectors is not necessary in this case.
In the past, efforts were made to simplify the structure of parabolic trough-shaped concentrators so as to lower the costs of a plant. For example, sheets and other thin-layer mirrors, such as anodized aluminum sheets or polymeric films, have been used for reflectors. Compared to composite glass, this entailed a significant reduction in weight. It is a disadvantage, however, that these thin-layer mirrors do not have the self-supporting properties of composite glass. Therefore, sophisticated support structures are required that support the thin-layer mirrors such that they are maintained in a parabolic shape. Additionally, the width of the aperture has to be increased when using these thin-layer mirrors, since the reflection of solar radiation is somewhat less for aluminum sheets and films than for silver-coated optical glasses. The large aperture widths of these concentrators offer a large area of attack to wind so that strong support structures are required. However, known support structures of aluminum or steel are very complicated and heavy, which makes them correspondingly expensive. U.S. Pat. No. 4,243,019 that forms the precharacterizing part of claim 1, describes a trough-shaped solar concentrator comprising two side members between which a corrugated support element extends in the longitudinal direction, a reflective surface being attached on the support element. Struts are fastened to the transverse faces of the side members, the struts being connected with a receptacle surrounding an absorber pipe. The receptacle is mounted for rotation on a stand so that the entire concentrator may be moved to track the course of the sun. Since the axis of rotation of the concentrator, which coincides with the axis of the absorber pipe, is disposed far above the supporting structure of the concentrator, a sophisticated stand structure is necessary and a great torque has to be applied to make the concentrator track the course of the sun.
It is another problem of large aperture widths that the distances between the individual troughs have to be rather great so that no shadows are cast in the morning and in the evening (given a north-to-south orientation). For a more effective exploitation of the given surface areas and for a reduction of the wind stresses, trough-shaped concentrators of facet structure have been proposed. With such a facet structure, the concentrator is divided into a plurality of segments arranged side-by-side on one level. These segments track the sun individually so that the solar radiation reflected by this segment is always concentrated onto the absorber. Also with the facet structure, the design of the support structure for the reflector poses some problems, because the support structure has to shape the reflector while being rigid at the same time to prevent torsion in the reflector. Prior support structures are of complicated design and are heavy, increasing the costs of a solar power plant.